This invention relates to universal joints. More particularly, this invention relates to a tripod constant velocity joint having chain-linked rollers to provide continuous rolling plunge travel.
Front wheel drive automobiles have a pair of halfshaft assemblies to transmit the power from the vehicle's transaxle to its front wheels. These halfshaft assemblies are normally comprised of two constant velocity joints with an interconnecting shaft connecting the two joints.
One of the constant velocity joints is a fixed joint. This joint has a fixed center of rotation and is capable of articulating to angles of 45.degree. to 50.degree.. This joint is placed at the wheel side of the vehicle. The large angular capacity of the joint allows the front wheels to accommodate steering angles as well as suspension movements.
The other constant velocity joint comprising the halfshaft assembly is a plunge joint. This joint has a movable center of rotation and is capable of angles of 20.degree. to 25.degree.. This joint is placed at the transaxle side of the vehicle. The movable center or plunging capability of this joint compensates for vehicle build tolerances as well as suspension movements and engine vibrations.
The tripod version of the plunging joint is widely used throughout the automotive industry as the joint positioned at the transaxle. While the joint performs acceptably for a majority of vehicles, it is not without its problems. In vehicles which are highly sensitive to noise, vibration and harshness (NVH) issues, the tripod joint can create noticeable and objectionable vibrations.
Tripod joints are comprised of a tulip shaped outer member having an internal cavity, a spider member, three annular rollers and a plurality of needle bearings. The spider member has three radially extending cylindrical trunnions. An annular roller is positioned around each trunnion. A plurality of needle bearings are journaled between the annular roller and the cylindrical trunnion. This arrangement allows free rolling of the annular roller relative to the trunnion. This assembly of the spider member, annular rollers and plurality of needles is disposed within the internal cavity of the outer member.
When the joint is operating at a zero degree angle, any plunging of the joint is accommodated by the rollers rolling against a longitudinal surface of the internal cavity of the outer member. The axial forces generated in the outer member are low due to the free rolling of the annular roller against the longitudinal surface of the outer member.
When the joint is operating at an angle, the plane of the annular rollers becomes skewed relative to the plane of the internal cavity. This skewed relationship inhibits true rolling action of the annular roller and a sliding action is introduced between the annular roller and the wall of the internal cavity of the outer member. As the angle of the joint increases, the amount of sliding also increases. This sliding action of the annular roller against the sidewall of the outer member produces a three per revolution pulsating load. The level of the load increases with the sliding action of the annular roller which increases with an increasing angle. Eventually, this pulsating load will become noticeable and objectionable to individuals riding in the vehicle. This objectionable vibration has been termed "shudder".
Numerous designs of tripods have been developed which attempt to reduce or eliminate this shudder phenomena. Some designs utilize a multi-piece roller system in an attempt to limit the amount of skewing of the roller which is in rolling contact with the outer member. These designs usually consist of an inner roller which rides on the trunnion and an outer roller which rides over the inner roller. A plurality of needle bearings is sometimes present between the inner roller and the trunnion or between the inner roller and the outer roller. These joints have enjoyed a limited amount of success in reducing shudder. Unfortunately due to their complex roller assemblies, internal friction generation and limited ability to reduce shudder, these joints do not always reduce the shudder sufficiently to increase the NVH level of the vehicle to an acceptable level.
Other types of joints have addressed the shudder problem by separating the components within the tripod joint which are responsible for the angular and translational movement. These joints have been termed "triplan" joints. There are two styles of triplan joints, a needle triplan and a ball triplan. The needle triplan utilizes a plurality of needle bearings rolling between two planar surfaces for translational movement. The angular movement is accommodated by matching partial spherical surfaces between two components. The ball triplan utilizes a plurality of ball bearings rolling between two partial cylindrical surfaces for translational movement. The angular movement is also accommodated by mating partial spherical surfaces of two components. While these joints are extremely successful in eliminating shudder they still have their problems. The internal components of the joint are expensive and the amount of rolling plunge available to these joints is only enough to accommodate engine vibrations and minor suspension movements. When larger suspension movements are encountered, the joint accommodates these large movements by reverting to a sliding not rolling action.
Positioning devices have been designed for both the needle and ball triplan joints in order to eliminate or reduce the amount of sliding travel encountered by these joints. While these are successful at expanding the use of these joints, they add to the already high cost and are not capable of eliminating the need for sliding travel in the joint.
Additional joints have been designed which utilize a recirculating plurality of needle bearings. The needle bearings roll between a planar surface on an inner member and a planar surface on the outer member. The inner member is designed to continuously guide the needle rollers in a continuous path around the inner member. This continuous supply of needle bearings between the inner member and the outer member eliminates the limited plunge problems associated with the needle triplan joints. While these joints provide excellent performance in reducing the shudder phenomena, they are complicated and difficult to assemble as well as expensive.
Accordingly, what is needed is a tripod constant velocity joint which provides unlimited rolling plunge while simplifying assembly and reducing costs.